Cytomegaloviurs (CMV) is a DNA virus in the family Herpesviridae. After primary infection, CMV becomes latent with potential for future reactivation ofthe latent virus. Cytomegalovirus (CMV) is the most important source of morbidity from an infectious pathogen following lung transplantation, causing deleterious direct effects (pneumonia) and indirect effects, such as enhanced rejection ofthe donor lung (allograft). The limiting factor in the long-term survival of lung transplantation patients is allograft rejection. Multiple studies have confirmed a strong association between CMV infection and rejection. CMV-specific T-cell responses are very important in controlling CMV replication, but very little investigation has been done in evaluating the role of CMV-specific T cell-mediated immunity in the context of rejection, particularly for lung allografts. The central objective of this proposal is to determine if the measurement of CMV-specific T cell responses in lung transplant patients can be used as a predictor ofthe risk of allograft rejection and poor control of CMV load. The aims ofthe study are: 1. Determine if circulating CMV-specific T-cell responses predict protection from lung allograft rejection in transplant recipients. 2. Determine the relationship of lung allograft rejection with subclinical CMV infection in the blood and lung. 3. Determine the role of CMV-specific T-cell responses in the lung for predicting protection from lung allograft rejection and decreased lung viral load. Results from the proposed studies of CMV-specific T-cell responses and viral load may allow improvement of current anti-viral strategies, and will provide new knowledge about the relationship behween CMV replication and allograft rejection. Conducting this study and completing the career development activities will allow this candidate to be well-positioned to establish an independent clinical research career focusing on application of new discoveries in viral pathogenesis and anti-viral immunity to the benefit of immunocompromised and healthy children with viral infections. RELEVANCE (See instructions): Cytomegalovirus (CMV) is a ubiquitous viral infection, which is asymptomatic in healthy people but causes significant disease in immunocompromised patients, such as neonates (congenital CMV) and transplant recipients. Increased knowledge from this proposal about T-cell immunity to CMV in a lung transplant patient may be applicable to other populations (e.g. neonate) and may be useful for CMV vaccine development.